As described on pages 99 to 134 in Nonpatent Document 1, for example, conventional electric vehicle controllers generally perform so-called vector control. In the vector control, an AC vector flowing in an AC motor is managed and controlled by dividing the AC vector into a magnetic flux component and a torque component in a rotating coordinate system.
Generally, an induced voltage of an AC motor is proportional to a product of a rotating speed of the AC motor and a magnetic flux thereof. The induced voltage becomes uncontrollable when it exceeds the maximum voltage that the controller can output. To ensure that the induced voltage does not become uncontrollable, it is common to perform a control in AC motors to weaken the magnetic flux than a rated magnetic flux in a high speed area. In electric vehicle controllers, following is control is performed for decreasing a switching loss in a power converter of a control device. That is, a one-pulse mode in which only switching is performed twice in 360 degrees in electrical angle of an AC-voltage command fundamental wave to output a rectangular wave voltage fixed to a maximum voltage that the control device can output is used for a high speed area. As described in Patent Document 1, for example, a secondary-magnetic-flux command value is obtained by an arithmetic operation and the obtained value is used for the control so that magnetic flux control and toque control are stably achieved during the one-pulse mode.
Patent Document 1 specifically describes an operating relationship between a magnetic-flux command value Φ2*2 and a voltage |V|. That is, in a speed area where a rated magnetic flux can be output, the magnetic flux command value is set to be a magnetic flux command of a constant rated value, so that the voltage |V| rises along with the rotating speed. When the voltage |V| reaches an output-controllable maximum voltage, the one-pulse mode is activated. While the voltage is fixed at the maximum value, the magnetic-flux command value is controlled to be small according to the rotating speed by Equation (6) in Patent Document 1.
Meanwhile, Patent Document 2 describes a method to minimize a total sum of a primary copper loss, a secondary copper loss, and a primary iron loss of an induction motor. In this method, a magnetic-flux command value is calculated relative to a torque command value and the induction motor is controlled based on the calculated magnetic-flux command value.    Patent Document 1: Japanese Patent Application Laid-open No. H11-285299    Patent Document 2: Japanese Patent Application Laid-open No. H7-322700    Nonpatent Literature 1: “Theory and Designing Practice of AC Servo System”, written/edited by Hidehiko SUGIMOTO, Sogo Denshi Publishing